linux-kernel - Re: utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps)

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Date:   Wed, 24 Aug 2016 18:56:37 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Rik van Riel <riel@...hat.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Sonny Rao <sonnyrao@...omium.org>, Jann Horn <jann@...jh.net>,
        Robert Foss <robert.foss@...labora.com>, corbet@....net,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        John Stultz <john.stultz@...aro.org>,
        ross.zwisler@...ux.intel.com, jmarchan@...hat.com,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Robin Humble <plaguedbypenguins@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        eric.engestrom@...tec.com, Janis Danisevskis <jdanis@...gle.com>,
        calvinowens@...com, Alexey Dobriyan <adobriyan@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        ldufour@...ux.vnet.ibm.com, linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Zhang <benzh@...omium.org>,
        Bryan Freed <bfreed@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>
Subject: Re: utime accounting regression since 4.6 (was: Re: [PACTH v2 0/3]
 Implement /proc/<pid>/totmaps)

On Tue 23-08-16 17:46:11, Rik van Riel wrote:
[...]
> Does the workload consistently get zero user
> time?

root@...t1:~# for i in $(seq 20); do /usr/bin/time -v awk '/^Rss/{rss+=$2} /^Pss/{pss+=$2} END {printf "rss:%d pss:%d\n", rss, pss}' /proc/3028/smaps; done 2>&1 | grep "User time" | sort | uniq -c
     20         User time (seconds): 0.00

sounds like pretty much consistent bad luck to me. I've attached the
single awk strace run, maybe this will help you understand the timing...

[...]

> Do I need to do anything special to reproduce
> your bug, besides running the max mmap program
> and the awk script?

That's how I noticed this. Nothing special really need. I am running
that in a kvm virt. machine but the bare metal gives me the same
results.

-- 
Michal Hocko
SUSE Labs

Download attachment "awk.strace.gz" of type "application/gzip" (328871 bytes)